When Cu is used as a catalyst, it is typically active in hydrogenation-dehydrogenation reactions. Cu metal which is activated in an atomic state by dissociative adsorption of hydrogen molecule thereon may be used as an active material for hydrogenation along with a noble metal such as Pt, Pd, Re or the like. If the hydrogen adsorption strength of the active material for hydrogenation is too large, it may be hydrocracked, and is undesirably hydrogenated while breaking the C—C bond of the hydrocarbon. Hence, it is necessary that hydrogen be appropriately adsorbed.
The Cu based catalyst is applied to hydrogenation or dehydrogenation in the relatively low temperature range (200-400° C.). In particular, the Cu based catalyst is known to have superior capability in terms of hydrogenation for synthesizing alcohol from carboxylic acid, water-gas shift reaction for making synthesis gas of carbon monoxide and hydrogen from hydrocarbon and water or carbon and water, methanol reforming for producing hydrogen from methanol and CO2 hydrogenation for synthesizing methanol from hydrogen and CO2 as opposed thereto, hydrodechlorination for removing Cl from Cl-containing hydrocarbon, and production of γ-butyrolactone from 1,4-butanediol (1,4-BDO).
Also a variety of methods of preparing a Cu based catalyst are known. Korean Laid-open Patent Publication No. 2010-0006249 discloses a heterogeneous Cu nanocatalyst, a method of preparing the same, and the use thereof in which the heterogeneous nanocatalyst includes Cu nanoparticles immobilized to a boehmite support.
Korean Laid-open Patent Publication No. 2007-0028102 discloses a method of preparing a nano-sized Cu—Mn oxide catalyst, comprising dissolving a manganese nitrate hydrate and a copper nitrate hydrate in distilled water, adding urea to the resulting solution so that urea is dissolved therein, adding a support to the solution with stirring in a neutral atmosphere, and drying, grinding and burning the stirred solution.
However, methods of efficiently preparing the nano-sized Cu based catalyst are still insufficient.
On the other hand, carboxylic acid obtained from fermenting biomass is used as a starting material for the preparation of alcohol, ketone, ester, and aldehyde, and is regarded as important in the chemical and energy industries. In particular, alcohol which is being increasingly used as a fuel as well as a chemical material is produced in a larger amount by a biological process including fermenting biomass which is environmentally friendly, in the production of petrochemicals.
The process of preparing alcohol comprising pretreating biomass and fermenting it requires a relatively long period of time because the biomass is converted into alcohol via a carboxylate using a pure biological process.
US Patent Application No. 2008/0248540 discloses the use of biological fermentation and chemical conversion via catalysis thus increasing the production yield of butanol and shortening the preparation time. In particular, butyric acid resulting from fermentation is esterified and then reacted with alcohol in the presence of an acid catalyst, thus preparing alkylbutyrate ester, which is then hydrogenated in a high-pressure hydrogen atmosphere using hydrocracking, thereby preparing the corresponding alcohol.
When butanol is prepared from butyric acid, butyric acid is reacted with butanol to form butyric acid butyl ester (or butylbutyrate), followed by performing hydrocracking thereby preparing butanol, which is represented below.
1 Step: butyric acid+butanol→butyric acid butyl ester+water (esterification)
2 Step: butyric acid butyl ester+hydrogen→butanol (hydrocracking)
The above esterification is carried out under low temperature (100-200° C.) and low pressure (5 bar) conditions using a batch reactor or a continuous flow reactor in the presence of an acid catalyst such as an ion exchange resin catalyst, a zeolite catalyst or the like, and the hydrocracking is carried out in a high-pressure hydrogen atmosphere. Thus, the preparation of butanol from butyric acid is conducted through two-step catalytic reactions and the catalysts used in the respective reactions should have different functions.
Because alcohol used for the esterification is excessively supplied from the outside (the molar ratio of alcohol/butyric acid=5 or more), the volume of the reactor should be increased and an additional process for separating, purifying and re-circulating the unreacted alcohol is required. In particular, the equilibrium conversion of the esterification depends on the reaction conditions and thus in order to increase the yield of butanol it is important that the reaction conditions be set so that a high equilibrium conversion is ensured. Also in the hydrocracking, the reaction becomes favorable as the hydrogen partial pressure increases, and the unreacted ester is difficult to separate from alcohol, and thus additional purification and recovery are required.
PCT WO 2008/070561 discloses a process of preparing an alcohol mixture, comprising pretreating and fermenting biomass thus producing a carboxylate mixture or a carboxylic acid mixture which is then reacted with a high-molecular-weight alcohol to thus be converted into ester, and then performing hydrogenation. This process requires two-step catalytic processes in order to produce alcohol. For example, ammonium acetate is reacted with heptanol which is a high-molecular-weight alcohol, thus preparing acetic acid heptyl ester, which is then treated in a high-pressure hydrogen atmosphere, yielding ethanol and heptanol. This reaction is represented as below.
1 Step: ammonium acetate+heptanol→acetic acid heptyl ester+water+ammonia (esterification)
2 Step: acetic acid heptyl ester+hydrogen→ethanol+heptanol (hydrocracking)
This process should include an additional step for removing ammonia in addition to the step for the typical esterification. If the reaction takes place at a temperature range falling outside of an appropriate temperature range in a state of ammonia not having been completely removed, acetamide is formed as a by-product.
The above process converts carboxylic acid into the corresponding alcohol using the two-step reactions.
In order to simplify the two-step catalytic reactions, Korean Laid-open Patent Publication No. 2009-103720 discloses the use of both a carboxylic acid and an alcohol as reactants so that esterification and hydrogenation are simultaneously carried out in a reactor thereby simplifying the complicated process.
Also, Korean Laid-open Patent Publication No. 2009-0049656 discloses a method of preparing n-butanol using direct hydrogenation of butyric acid in the presence of a catalyst comprising a Cu based catalyst and a diluent such as silica, alumina, titania and zinc oxide. This patent is problematic because the amount of diluent relative to Cu is restricted.
The process of preparing alcohol from a carboxylic acid which is produced by fermenting biomass is known. In the process, the catalyst used to prepare alcohol from a carboxylic acid is mainly a commercially available Cu catalyst.
In the case of the commercially available Cu catalyst, its activity is undesirably low for a carboxylic acid having high acidity such as acetic acid.
The catalysts used to prepare ethanol from acetic acid are known to be Pt and Sn supported on silica as disclosed in US Patent Application No. 20100121114. U.S. Pat. No. 4,990,655 discloses a catalyst comprising a graphite carbon support and an active component composed of a Group 8 noble metal and Re in order to prepare ethanol or propanol from acetic acid or propionic acid.
The currently available catalysts are unsatisfactory when preparing alcohol from an acid mixture comprising two or more carboxylic acids including a carboxylic acid having high acidity such as acetic acid.